The present invention relates to a grinding apparatus using a fluid servomotor such as pneumatic or oil hydraulic servomotor which is supplied with pressurized fluid controlled of its flow rate by means of a servo valve as driving fluid.
A fluid servomotor device which controls the rotation speed of the load such as grinding wheel, etc. using a fluid motor, was well known in the art. FIG. 7 is a block diagram showing an example of a fluid servomotor of prior art.
In FIG.7, reference numeral 34 is a fluid motor driven by fluid supplied from a fluid source 32 via a servo valve 33, reference numeral 36 is a grinding wheel driven by the fluid motor 34.
The fluid motor 34 is connected to the fluid source 32 via the servo valve 33. The rotational speed of the fluid motor 34 is controlled by the signal inputted to the servo valve 33.
The rotation of the output shaft of the fluid motor 34 is transmitted through gears 37 to a tachogenerator 35, a rotational speed detector. The tachogenerator 35 outputs a voltage proportional to the rotation speed of the fluid motor 34. Reference numeral 31 is a control device, which determines the signal to control the servo valve 33 by calculation based on the voltage signal from tachogenerator 35 and a prescribed rotation speed 30, and output the determined signal.
Through this series of operations, the control of the rotational speed of the grinding wheel 36 connected to the fluid motor 34 is realized. Thus, the fluid motor 34 functions as a servomotor.
In the servomotor device of the prior art, the servomotor 34 and the tachogenerator 35 which is a rotational speed detector, are constructed as separate entities. So, in the case the device is used as a servomotor, a means for transmitting rotation to the rotational speed detector (tachogenerator) 35 must be provided outside the servomotor 34 to detect the rotational speed. Therefore, in the case of, for example, controlling the output of a fluid motor 34 of cylinder diameter of about 30 mm, a rotational speed detector (tachogenerator) 35 of about the same size as the fluid motor 34 is necessary. Thus the configuration of the device becomes large and its downsizing is difficult.
There are also problems in the device of prior art that the rigidity of the control mechanism is lowered by the influence of the backlash in the rotation transmitting mechanism such as gear, timing belt, chain, etc., which causes oscillation.
These problems are important in the case a grinding apparatus is composed by attaching a grinding wheel to the output shaft of a fluid motor.
In the case a fluid motor is used as the driving source of a grinding wheel, a grinding apparatus which needs no consideration for explosion proof and short circuit of electric wiring due to grinding lubricant, etc., which consideration is needed in the case with an electric motor, is possible to be provided, but the rotation speed and output can not be controlled freely by the control of voltage and current as in the case with an electric motor, and so a contrivance is necessary.
An object of the present invention is, for solving the problems mentioned above, to provide, in the case a grinding apparatus is composed by attaching a grinding wheel to the output shaft of a fluid servomotor, a grinding apparatus which enables grinding with good efficiency concerning the grinding wheel, with a rotational speed detecting means integrated into the motor.
Another object of the present invention is to provide a grinding apparatus which is able to be freely set to a rotation control range whereby grinding is performed with good efficiency concerning the grinding wheel, or to a range whereby the wear of the grinding wheel is prevented.
To solve the problems, the present invention provide a grinding apparatus, in which a grinding wheel is attached to the output shaft of a fluid servomotor having a fluid motor driven by the fluid supplied from a fluid source and controlled through a servo valve, and the motor housing of the servomotor is mounted on a stage capable of being moved in the direction of pressing the servomotor against the work to be ground, characterized in that;
the output shaft of the servomotor is extended through a cover attached to the output side of the fluid motor along the center line of the cover;
a rotating member forming a part of a rotation detector is fit on the output shaft inside the cover, and a rotation detecting member is attached to the cover inside the same facing the rotating member; and
the difference between the rotational speed of the output detected by the detecting member and the aimed rotation speed is determined by a control device, and the stage is able to be moved based on the output control signal from the control device.
According to the present invention, as the rotational speed detecting means is provided inside the cover joined to the motor housing so as to make it integral part of the fluid servomotor, the integral unit can be mounted on the stage as it is. So, the grinding apparatus is largely downsized and spatial limitation when the fluid motor is mounted on the stage is eliminated. This increases the freedom of design of fluid motor and a smaller sized, larger output fluid servomotor device compared to that of prior art can be obtained, which is particularly effective for a large grinding apparatus in which fluctuation of the grinding wheel is large.
Further, as the rotating member of the rotation speed detecting means is attached directly to the output shaft of the fluid motor, the occurrence of backlash in the rotation transmitting means of a servomotor of prior art is excluded. As a result, chattering on the side of the grinding wheel, lowering of working rigidity, oscillation, etc., are avoided and grinding performance increases.
As the rotation speed detecting means is provided inside the cover, the danger of malfunction of the detecting means due to grinding powder or grinding lubricant acting as noise is excluded, and the detection of the rotational speed is possible with good accuracy.
Still further, it is suitable to compose so that, for increasing the grinding efficiency of the grinding wheel attached to the output shaft, the aimed rotation speed is set at the speed range of maximum output and grinding is performed with increased pressing force of the grinding wheel against the work to be ground, or to compose so that, for preventing the wear of the grinding wheel attached to the output shaft, the aimed rotation speed is set at the high speed range and grinding is performed with decreased pressing force of the grinding wheel against the work to be ground. Thus, grinding is possible in accordance with various grinding conditions.
It is suitable, for attaining the object of the present invention nicely, that the rotating member attached to the output shaft inside the cover is the rotor of a tachogenerator, or the disk plate of an optical rotary encoder, or the magnetic ring of a magnetic rotary encoder, and the rotation speed detecting member attached to the cover inside the same is the magnetic body of the tachogenerator, or the photointerrupter of the optical rotary encoder, or the hall IC of the magnetic rotary encoder.